Leading architects and engineers are calling for all-glass skyscrapers to be banned because they are too difficult and expensive to cool.
"If you're building a greenhouse in a climate emergency, it's a pretty odd thing to do to say the least," said Simon Sturgis, an adviser to the governmentand the Greater London Authority, as well as chairman of the Royal Institute of British Architects sustainability group. "If you're using standard glass facades you need a lot of energy to cool them down, and using a lot of energy equates to a lot of carbon emissions."
Glass-fronted offices, from high- profile buildings like the Shard to shopping centres and industrial parks, have become popular with architects and their clients because they create an arresting view in a city skyline, let in lots of natural light and provide great views for those inside. But the sunlight also brings heat, and in sealed buildings there is nowhere for it to escape to naturally - something which, as Britain sweltered in a record-breaking heatwave last week, will have become apparent to many working inside them.
To avoid this greenhouse effect, air conditioning has been the standard solution. But that is problematic in itself. The International Energy Agency estimates that about 40% of global carbon dioxide emissions come from constructing, heating, cooling and demolishing buildings. Air conditioning is a growing proportion of this: energy used on cooling has doubled since 2000 and accounts for about 14 per cent of all energy use now.
In April the mayor of New York, Bill de Blasio, said he would ban all-glass buildings and force developers to retrofit existing buildings to make them more energy-efficient, although the "ban" was later clarified to mean excessive use of glass and steel.
Sadiq Khan, the mayor of London, has ruled out such a plan for the British capital, but Sturgis believes the American is on the right lines. "Certainly, I think there should be a ban," he added. "The connection needs to be made between the climate emergency and all-glass buildings. But the connection hasn't been made yett."
Martin Fahey, head of sustainability at Mitsubishi Electric, warned that higher temperatures meant that air conditioning machines now needed to work harder than in the past. "Most air conditioning equipment is designed to give an internal temperature between seven to 10 degrees lower than the ambient temperature," he said. "I suppose it's fair to say if that machine is getting old or has developed a fault somehow, Murphy's law being what it is, something will go wrong and it will fail."
The new version of the London Plan, the rules for all development in Greater London, which is due to take effect next spring, will require construction firms to make an assessment of a building's energy use across its whole life-cycle. Sturgis hopes that investors will react more quickly.
"Big commercial tenants don't like standing up in front of their shareholders and saying they're doing embarrassing things," he said. "No one wants to be treated as ‘Mr Climate-Dirty building' and I think this is going to start happening.
"I'm advising a bank that wants to build a very big building in London - which I can't tell you about, but I'm having this exact conversation - I think the building could be obsolete by the time it's finished."
Glass has some advantages: in colder weather, the warming effect of sunshine - "solar heat gain" in the jargon - means less energy on heating. Architects can still use this with smaller windows, according to Simon Wyatt, a partner at Cundall, an engineering firm, and a UK Green Building Council committee member. He said natural ventilation would save "up to 60 to 70 per cent on our air conditioning loads" but in city centres, air pollution and traffic noise make this impossible.
Newer buildings use special types of glass that can become more opaque to block sunshine in hot weather, or even generate electricity themselves, such as the Edge building in Amsterdam. It uses about 70 per cent less energy than most buildings but is not glass-fronted on all sides - the southern, eastern and western sides have smaller window openings to reduce heat gain, and openable windows.
But these laminated glass panels still contribute to the climate crisis, according to Sturgis, because they are much more expensive to make and almost impossible to recycle.
"To mitigate the amount of energy used to cool these buildings, you have to produce a really complicated façade, which is usually triple glazed," he said. "But double glazed units and laminated glass don't last very long - 40 years or so. So you have to replace your facade every 40 years, that's also not a very good idea."
